Problem: Simplify the following expression: $n = \dfrac{2y}{7} + \dfrac{7y}{3}$
Solution: In order to add expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $7$ and $3$ $\lcm(7, 3) = 21$ $ n = \dfrac{3}{3} \cdot \dfrac{2y}{7} + \dfrac{7}{7} \cdot \dfrac{7y}{3} $ $n = \dfrac{6y}{21} + \dfrac{49y}{21}$ $n = \dfrac{6y +49y}{21}$ $n = \dfrac{55y}{21}$